Field of the Invention
The invention relates to an automatic transmission that includes planetary gear mechanisms and engagement mechanisms.
Description of Related Art
An automatic transmission that includes planetary gear mechanisms having multiple elements rotatable inside a casing, and multiple engagement mechanisms switchable to a coupled state in which the elements are coupled to one another, or switchable to a fixed state in which the elements are fixed to the casing has been known.
As one of the engagement mechanism, it has been known that such an automatic transmission uses a switching mechanism (a two-way clutch, for example) that is switchable between the fixed state and the reverse rotation preventing state which allows the normal rotation and prevents the reverse rotation of the elements of the planetary gear mechanisms. In such a switching mechanism, a hydraulic pressure control circuit, etc. perform the switching (refer to Patent Literature 1, for example).